Paris - Serge and Beate Klarsfeld are not only Europe's most famous Nazi hunters. For more than five decades, they've been the vigilante enforcers of the continent's moral conscience.

The husband-and-wife team - through painstaking research and often daring exploits - has tracked down murderers from the suburbs of Damascus, Syria, to the jungles of Bolivia. They pushed for the arrests and ultimate convictions of former Nazis and French collaborators such as Maurice Papon, Paul Touvier and Klaus Barbie, known as the Butcher of Lyon. And they have documented the stories of thousands of French Jews sent to the Nazi gas chambers.

Their mission has been to seek justice but also to force a European reckoning with questions of complicity and culpability in a war many people preferred to forget. It was largely their influence that prompted President Jacques Chirac, soon after taking office in 1995, to acknowledge that "France, home of the Enlightenment and the Rights of Man . . . broke her word and delivered the people she was protecting to their executioners."

Yet today, at the respective ages of 82 and 79, Serge and Beate Klarsfeld say they are horrified by the state of affairs in Europe and beyond: the rise of right-wing populist movements, and now governments, across the continent, often fueled by support from young voters. The parallel forces of nationalism and xenophobia, once again permissible in the public sphere. The apparent desire - from Poland to the United States - to play with the truth of the past so as to alter the norms of the present, the norms the Klarsfelds spent decades upholding.

"The young today don't know hunger. They don't know war," Serge said in an interview at the Klarsfelds' office, reclining at a desk piled high with the kind of documents he and his wife have used for years to build their dossiers. "They don't know that the European Union brought to Europe so much, and they don't know that the generation that came before them worked so hard for what there is."

To that end, the Klarsfelds are publishing an English translation of a joint memoir. In "Hunting the Truth," sections written in their alternating voices tell the story of a marriage and a common purpose.

"People are often very passive and believe they can't do anything," Serge said. "But they can do something, and so we're explaining that we are people who did something."

Born into a Jewish family in Bucharest in 1935, Serge emigrated to France along with his parents and sister before the outbreak of World War II.

The family was living in Nice when the Gestapo arrived on the night of September 30, 1943. The soldiers arrested his father, Arno, as the 8-year-old Serge hid with his mother and sister behind a false closet his father had built precisely for this moment. The last words Arno whispered to them were "my keys," which he used to lock the door on his way out, so the Nazi officers would not suspect that anyone was left inside.

Arno Klarsfeld died in Auschwitz.

Beate, by contrast, said she knew next to nothing of the Holocaust before she moved to Paris and met Serge.

She was born in Berlin in 1939, the daughter of working-class, Protestant parents who voted for Hitler in 1933. Her father later served as an infantryman in the German army. "I used to recite little poems for the führer at my kindergarten," she recalls in one of her portions of the memoir.

As for her parents, during and after the war: "They had neither learned nor forgotten anything from the epochal events they had sleepwalked through. . . . They did not feel any responsibility for what had occurred under Nazism."

Serge and Beate met by chance on the Paris Metro on May 11, 1960 - on the same day, the Israelis kidnapped Adolf Eichmann outside Buenos Aires. Beate remembers Serge's suit: three pieces, Prince of Wales check. Serge remembers her dress: blue, cinched at the waist.

He was a 24-year-old student; she was a 21-year-old au pair, and several stations went by before Serge could muster the courage to speak to Beate, who could barely speak French back then. Three days later they went to the movies. Three years later they were married.

"When she was confronted with the image of Nazi Germany, she accepted it," Serge writes. "But I could already feel the resolve accumulating within her to react against that image, not through denial, but through positive action."

It was Serge's personal experience that framed what became the couple's career.

In the memoir, he puts it this way: "If the child who had survived the genocide by a miracle, and by his father's sacrifice, remained deaf to that scream . . . wouldn't my life be an act of betrayal?"

But it was ultimately Beate's daring that vaulted the Klarsfelds into the international spotlight and established the Franco-German duo as Europe's leading Nazi hunters.

In 1968, she publicly slapped Kurt Kiesinger, then the chancellor of West Germany and a former Nazi propaganda official, in the face.

Asked about what was going through her mind in that moment, she reached down to pet one of the couple's two small dogs curled beneath her chair. She said only that she seized the moment - and that she left her mark. "He grabbed his eye and asked for a doctor," she said. Within a year, his political career was finished.

She has been detained in or deported from a number of countries: among others, Bolivia, the former Czechoslovakia and Syria, where she arrived in a wig and an assumed name in hot pursuit of Alois Brunner, a Nazi leader and former assistant of Adolf Eichmann, who had overseen the deportation of thousands of Jews from France - including Serge's father.

Undeniably, however, the Klarsfelds's biggest catch was Barbie. In April 1944, the SS operative notoriously ordered the deportation of 44 Jewish orphans from Izieu, a small town in eastern France. But U.S. intelligence services helped him escape to Bolivia after the war, in exchange for assistance with anti-Marxist activities.

The Klarsfelds learned of his whereabouts in the early 1970s and successfully lobbied for his extradition to France in 1983, after Bolivia's dictatorship collapsed and Barbie no longer enjoyed the regime's protection. He was convicted of crimes against humanity and died in prison in Lyon in 1991.

"All my troubles in the past started when Madame Klarsfeld came to Bolivia," Barbie reportedly said on the first day of his trial.

Robert Paxton, an American historian whose study of the Vichy government in the 1960s was among the first to expose the extent of French collaboration with Nazi Germany, said that the Klarsfelds - "although their memoirs never mention any other historians positively" - have ultimately had an affect on the subject that cannot be understated.

It is largely thanks to the Klarsfelds, Paxton said, that Paris streets now display some of the capital's most haunting memorials: the black plaques on the former schools from which Jewish children were deported during the war.

"They've had an enormous impact in public relations terms, and in a very major way," he said, noting also that he and the couple have had their share of academic disagreements over the years, including over the activities of the Catholic Church in France during the war. But Paxton admires the way the couple have assumed their role as moral arbiters in contemporary France. "They've done it with great thoroughness and great care."

Despite their successes, the Klarsfelds eschew self-congratulation. There simply isn't time. "We fight for values that we will defend the rest of our lives," Serge said. "After we die, we can't say what will happen."